1. Field of the Invention
The present invention relates to a boat propulsion system, a control device for the boat propulsion system to which a steering wheel device, a remote control device, and the like for operating the boat propulsion system are electrically connected, and a boat including the control device for the boat propulsion system.
2. Description of the Related Art
When a crankshaft rotates in a reverse direction, the directions of intake air and exhaust gas are reversed in a boat propulsion system provided in the boat for providing a propulsive force to a hull by rotating a propeller or the like. Consequently, water flowing in a reverse direction from an exhaust pipe extending into the water enters a cylinder of an internal combustion engine during running. Therefore, a control device for a running condition for the boat which senses a reverse rotation of the crankshaft is necessary in order to prevent water from entering the engine.
As a conventional control device for a running condition for a boat of this type, there is a control device described in JP-A-2003-120397 and JP-A-Hei 9-79125. Specifically, JP-A-2003-120397 describes a control device for a boat propulsion system (a reverse rotation prevention device), including an internal combustion engine provided with a crankshaft which converts movement in a reciprocating direction of a piston into movement in a rotational direction, in which the boat propulsion system providing a propulsive force to a hull is controlled by the drive of the internal combustion engine. The boat propulsion system further includes a control device cylinder discrimination device for discriminating a cylinder of the internal combustion engine, a crank angle signal generation device for generating a prescribed number of crank angle signals for each prescribed crank angle, a counter for counting the crank angle signals generated by the crank angle signal generation device, a count value multiple determination device for determining whether or not a count value of the counter is a multiple of the prescribed number when a cylinder is discriminated by the cylinder discrimination device, and an engine stop device for stopping the internal combustion engine or, specifically, for stopping ignition and fuel injection by determining that the internal combustion engine rotates in a reverse direction when it is determined that the count value is not a multiple of the prescribed number by the count value multiple determination device.
On the other hand, JP-A-Hei 9-79125 describes a control device for a boat propulsion system including a crankshaft provided with a crank which converts movement in a reciprocating direction of a piston into movement in a rotational direction, an injector in a section more upstream than the combustion chamber for injecting fuel with fresh air supplied to a combustion chamber via an intake air passage, a crankcase, a scavenge air passage, and a spark plug in the combustion chamber in which ignition is made at an ignition timing corresponding to an operating state on the basis of a pulse signal. The boat propulsion system further includes an internal combustion engine (two-cycle, fuel-injection type internal combustion engine), wherein the boat propulsion system providing the propulsive force to the hull is controlled by the drive from the internal combustion engine, and a reverse rotation sensing device of the engine is provided and ignition is stopped but fuel injection is continued when a reverse rotation is sensed.
In these documents, it is attempted to prevent water from entering the engine by stopping combustion in the engine when a reverse rotation of a crankshaft is sensed.
However, according to JP-A-2003-120397 and JP-A-Hei 9-79125, for example, when a gear of the boat is shifted from forward drive to reverse drive (or shifted from reverse drive to forward drive), a reaction force from a propeller is suddenly increased. Accordingly, the reaction force may become greater than the rotating torque of a crankshaft thereby rotating the crankshaft in a reverse direction. In a case like this, even after combustion in an engine is stopped, the propeller keeps rotating in a direction of reverse drive (or in a direction of forward drive) by an inertia force. Consequently, the inertia force is transmitted to the engine. Therefore, in the boat propulsion systems described in JP-A-2003-120397 and JP-A-Hei 9-79125, there is a problem in which water may enter the engine by drive of the engine resulting from the inertia force.
In addition, in JP-A-2003-120397 and JP-A-Hei 9-79125, since a complex mechanism and many sensors are necessary for sensing a reverse rotation of the crankshaft, there is a problem in which the manufacturing cost of the internal combustion engine is increased and necessary maintenance work becomes laborious. Moreover, when a special operation is performed in order to prevent water from entering the engine as described above, a special mechanism is necessary for performing such an operation. As a result, there is a problem in which the manufacturing cost of the internal combustion engine is increased and necessary maintenance work becomes laborious.